Serious deep mycosis such as invasive candidiasis can often be a fatal disease. In the past, it has been considered that the principal protective mechanism on the side of a host organism against fungi such as Candida is nonspecific immunization by neutrophils. When this protective mechanism functions normally there is little risk of becoming infected with fungi. However, in recent years, the risk of suffering from deep mycosis has been boosted because of the increased number of patients with underlying diseases decreasing the immunological function of the body, such as malignant tumors (in particular, hemopoietic malignant tumors such as acute leukemia or malignant lymphoma) and AIDS, frequent use of anticancer agents or immunosuppressants, heavy use of antibacterial antibiotics or steroid hormones, long-term use of central venous hyperalimentation or venous catheterization and the like (Non-Patent Document 1).
Agents used for the treatment of such deep mycosis are very few, when compared to antibacterial agents used, and include only amphotericin B, flucytosine, miconazole, fluconazole, fosfluconazole, itraconazole, voriconazole, micafungin and the like.
On the other hand, there is an increasing need for safe and effective agents against opportunistic fungal infections caused by fungal pathogens such as Candida, Cryptococcus and Aspergillus.
While the agents that are used at present, for example, amphotericin B, have an extremely strong fungicidal action, they have a problem regarding side effects such as nephrotoxicity, so that their clinical usage is limited. Flucytosine has problems with the development of resistance. Micafungin has a low activity against the Cryptococcus. Azoles such as fluconazole and voriconazole are most frequently used at present due to their balance between effectiveness and safety, although their fungicidal action is inferior to that of amphotericin B (Non-Patent Documents 2 and 3).
Methods for combination use of antifungal agents are being used for purposes such as to boost treatment effects (Non-Patent Document 4). Research is also progressing into the combination of antifungal agents (Patent Documents 1, 2 and 3). However, the number of agents being combined is limited, meaning that satisfactory treatment effects cannot be guaranteed.
Further, phenylamidine derivatives having antifungal activity are known (Patent Document 4).    Patent Document 1: Japanese Patent No. 3288051    Patent Document 2: JP-A-11-504931    Patent Document 3: JP-A-2003-527314    Patent Document 4: International Patent Publication No. WO2006/003881    Non-Patent Document 1: Rinsho to Biseibutsu (Clinics and Microorganisms), Vol. 17, pp. 265-266, 1990    Non-Patent Document 2: Rinsho to Biseibutsu (Clinics and Microorganisms), Vol. 21, pp. 277-283, 1994    Non-Patent Document 3: Rinsho to Biseibutsu (Clinics and Microorganisms), Vol. 30, pp. 595-614, 2003    Non-Patent Document 4: Diagnosis and treatment guideline of deep mycosis, PP. 20, 29, Ishiyaku Publishers, Inc., 2003